Excessive intake of fat and sugar is known to cause obesity, hyperlipemia and the like. Elevations of triglyceride (hereinafter, sometimes referred to as "TG") levels in blood in hyperlipemia are said to become a cause which brings disorders such as hypertension and arteriosclerosis. Then, a number of attempts to inhibit elevations of TG levels in blood have been made to improve obesity and hyperlipemia.
At present, in order to inhibit elevations of TG levels in blood, dietary restriction, intake of dietary foods (such as low calorie diet (LCD) or very low calorie diet (VLCD)) and administration of various pharmaceuticals are carried out. As such pharmaceuticals, for example, dextran sulfate which enhances lipoprotein lipase activity in blood, nicomol which inhibits lipid absorption, clofibrate and pravastatin which are lipid metabolism improving agents, and the like are used.
However, dietary restriction gives anguish to those who practice it and side effects caused by the administration of the above pharmaceuticals are also apprehended. Thus, development of an agent for inhibiting elevations of blood TG levels is desired which has a stronger effect of inhibiting elevations of blood TG levels and in which there is no apprehension about causing side effects.
On the other hand, at present, high calorie feeds are given to livestock and hatchery fish for promoting their growth. As a result, abnormalities in fat metabolism occur also in such livestock and fish, and TG levels in their blood tend to elevate. Due to these elevations of TG levels in blood, fat contents in livestock and hatchery fish become excessive. Thus, eating such livestock or fish leads to excessive fat intake. Furthermore, such livestock and fish have gradually failed to meet consumers' liking in taste. In addition, the increase in fat contents described above is a serious issue relating to a problem of waste of feeds and also relating to a problem of disposal of the fat attached to slaughtered bodies. Thus, inhibition of elevations of TG levels in blood has become an urgent need, in particular, in the stockbreeding industry and the fisheries industry in Japan.
Recently, a patent application has been filed for an oligopeptide-containing material developed by some researchers including one of the present inventors (International Publication No. WO420979A1; Japanese Patent Publication No. 5-87052), and a technology similar to this is disclosed in Japanese Unexamined Patent Publication No. 2-154693. Also, it has been made clear that specific oligopeptides have lipid metabolism improving effects including inhibition of elevations of TG levels in blood (Kyoichi Kagawa, Food Chemical Monthly, 6:80 (1990); Chizuko Fukuhama et al., FOLIA PHARMACOLOGICA JAPONICA, 97:38 (1991)).
The oligopeptide-containing material disclosed in the above patent publication, etc. is a mixture of proteolysates and, thus, an amino acid sequence for its truly active component (i.e., a peptide as its active component) has not yet been elucidated.
This suggests that the above peptide-containing material is low in purity as a pharmaceutical. Further, when this material is combined in a food, it is difficult to quantitatively determine the material separately from other peptides contained in the food and thus there is a problem of quality control. Therefore, it is necessary to ascertain the truly active component in the above peptide-containing material, i.e., the peptide inhibiting elevations of TG levels in blood as an active component.
Although Japanese Unexamined Patent Publication No. 7-188284 discloses a peptide inhibiting elevations of triglyceride levels in blood and an agent for inhibiting elevations of triglyceride levels in blood comprising the above peptide, the effect of inhibiting elevations of triglyceride levels in blood produced by the peptide or the agent is still insufficient.